Proinsulin
Proinsulin
Proinsulin (pronounced proh-IN-suh-lin) is a prohormone precursor to the hormone insulin produced by the pancreas.
Etymology
The term "proinsulin" is derived from the prefix "pro-" meaning "before" or "precursor," and "insulin," the hormone it precedes.
Definition
Proinsulin is a single-chain polypeptide consisting of three domains: an amino-terminal B chain, a carboxy-terminal A chain, and a connecting peptide, known as the C-peptide. These chains are connected by disulfide bonds. In the process of insulin synthesis, proinsulin is the first molecule to be produced.
Function
Proinsulin is synthesized in the beta cells of the islets of Langerhans in the pancreas. It is then stored in secretory vesicles where it is converted into mature insulin and C-peptide by the actions of the enzymes prohormone convertase 1 and prohormone convertase 2, along with the exoprotease carboxypeptidase E. The mature insulin and C-peptide are then stored in secretory granules and released into the bloodstream in response to an increase in blood glucose levels.
Clinical Significance
Proinsulin levels can be measured in the blood and are often used in the diagnosis and management of various medical conditions. Elevated proinsulin levels can indicate beta cell dysfunction and may be seen in conditions such as type 2 diabetes and insulinoma, a rare tumor of the insulin-producing cells of the pancreas.
Related Terms
- Insulin
- C-peptide
- Beta cells
- Islets of Langerhans
- Prohormone convertase 1
- Prohormone convertase 2
- Carboxypeptidase E
- Type 2 diabetes
- Insulinoma
External links
- Medical encyclopedia article on Proinsulin
- Wikipedia's article - Proinsulin
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